Apparatus detecting relative body movement

ABSTRACT

The invention relates to a measuring device for detecting a body moving in relation to an, in particular, tubular container. Said device comprises at least one magnet unit which generates a magnetic field, measures this magnetic field and which is assigned to the container and/or to the magnetic body. The device also comprises at least one evaluation device connected to the magnet units and provided for receiving measurement signals of the magnet units. The aim of the invention is to improve a measuring device of this type in order to be able to easily determine, in addition to the position of the body in relation to the container in a longitudinal direction, the position of the body in relation to the container in the transverse direction with a relatively high level of accuracy. To this end, the magnet units comprise a maximum magnetic flux that is essentially perpendicular to the direction of the relative motion of the body and container.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/752,751, filed May 23, 2007, which is a divisional of U.S.application Ser. No. 10/891,622, filed Jul. 15, 2004, now U.S. Pat. No.7,239,132, which is a divisional of Ser. No. 10/276,203, filed Nov. 12,2002, now U.S. Pat. No. 6,815,945, and further claims a right ofpriority based upon PCT Application No. PCT/EP01/05157, filed 7 May 2001and German Application No. 200 08 413.5 filed 7 May 2000, all of whichare hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

This invention relates to a detection system for sensing an object inmotion relative to a container, especially tubular in design, whereby atleast one magnetic unit is associated with the container and/or object,generating as well as measuring magnetic fields, and at least oneevaluation device is connected to the magnetic units and serves toreceive sensing signals from the magnetic units.

A detection system of this type is described in U.S. Pat. No. 3,103,976.That particular detection system is used in locating pipes, andespecially pipe ends to be joined, in underwater drilling and similaroperations. A guide tube, serving as a container extending between atopside derrick and a frame section anchored on the sea bottom, isequipped on its outside with a coil as the magnetic unit generating amagnetic field and with each two search coils respectively mounted aboveand below the first coil and serving as the magnetic-field measuringmagnets. Electric cables connect these various coils with a topsideevaluation unit within the derrick. The magnetic-held-generating coilproduces a magnetic field inside the guide tube essentially along thelongitudinal axis of the tube. That magnetic field also permeates thetwo magnetic-field-measuring coils. If and when within the guide tube adrill rod, tool, pipe or the like is shifted, the magnetic field inthese measuring coils will change as a function of the position of themoving object, leading to a corresponding induction in these coils. Itis thus possible to determine when the object concerned has reached oneof these magnetic-field-measuring coils or for instance the blowoutvalve located on the sea bottom.

That earlier detection system, however, is essentially limited tosensing the position only of the forward end of the moving object, withthe positional detection accuracy being determined by its distance fromthe coils which are mounted along the longitudinal axis of the guidetube, by the coil width in the longitudinal direction, and similarfactors.

BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS

It is the objective of this invention to provide an improved detectionsystem of the type first above mentioned, the improvement consisting inthe ability, in simple fashion and with a relatively high degree ofaccuracy, to determine not only the position of the object relative tothe container in the longitudinal direction but also its position in thetransverse direction relative to the container.

In conjunction with the characteristic features specified within themain concept of the claims, this is accomplished in that the magneticunits produce a maximum magnetic flux essentially perpendicular to thedirection of relative movement between the object and the container.This causes a change in the magnetic field and in the magnetic flux whenthe object is close enough to the container that both are located withinthe magnetic field of the magnetic-field-generating magnetic unit. Atthe same time, given this position of the object and the containerrelative to each other, there will be a change in the magnetic field inthe direction perpendicular to the relative movement, thus yielding forthe evaluation device additional information on the position of theobject and the container perpendicular to the direction of relativemovement.

According to this invention, the functionality of the detection systemdoes not depend on whether the container, for instance tubular indesign, is stationary while the object moves relative to it, or viceversa, for as long as at least the moving part contains a magneticelement which triggers a corresponding change in the magnetic fieldbetween the magnetic units.

In oil-drilling or similar operations, it may be advantageous in thiscontext if in particular the tubular container constitutes theaforementioned guide tube and the object is the part that moves relativeto that tube. The latter should consist of, or contain, a magneticmaterial at least at the point which is to serve for the detection ofthe position and orientation of the object relative to the container.That point could for instance be the forward end of the object.

An object of this type typically moves within the container so that thecorresponding magnetic units can be advantageously mounted in an insidearea of the container. On the other hand, if the moving object consistsof a non-magnetic material while the container is provided with amagnetic element in an appropriate location, the corresponding magneticunits may equally well be mounted on an outside surface of the object.It is also possible, for facilitated access, to position the magneticunits on an outside surface of the container with the generated magneticfield extending through the wall and into the interior of the container.

In one possible, simple configuration for the precise capture of themoving object the magnetic units are arranged along at least oneorientational plane perpendicular to the direction of relative movement.For example, multiple magnetic units may be arranged in a circular arrayor in some other way depending on the cross-sectional shape of thecontainer, with the possibility of mounting the magnetic units, withequidistant spacing from one another, in the circumferential directionof the container.

So as not to limit the detection of the object to essentially one suchplane, magnetic units may be mounted perpendicular to the direction ofrelative movement in evenly spaced planar increments. This permitscapture in each of these staggered planes as well as detection betweenthese planes by means of suitably interconnected magnetic units.

Depending on the design of the magnetic unit, it is possible for such amagnetic unit to be switchable between magnetic-field generation andmagnetic-field sensing. This can take place even during the course of ameasurement. Evidently, such switchability of the magnetic unitsinvolves variable polarity of the magnetic units, variablemagnetic-field intensity or the like.

A simple design example of a magnetic-field-generating magnetic unit canbe implemented in the form of a permanent magnet.

For an expanded range of possibilities in object detection per theabove, a magnetic unit may be constituted of an electrically poweredcoil which provides a simple way to permit operation both formagnetic-field generation and magnetic-field measurement. A coil alsoallows for easy variation of the magnetic-field intensity or polarityand the generation of alternating fields.

A magnetic-field-measuring unit that is at once precise, simple andinexpensive may be in the form of a magnetic-field sensor and inparticular a Hall element. Magnetic-field sensors of that type can beinstalled, in simple fashion and at low cost, in arrays of the desireddensity and configuration for instance on the inside of the container.

Of course, a suitably designed magnetic unit can also detect magneticattenuation instead of measuring the magnetic field or magnetic flux.

For an amplification of the magnetic field and thus of the magnetic fluxperpendicular to the direction of relative movement, the magnetic unitmay incorporate a magnetizable material, for instance a ferromagnetic orparamagnetic material.

To avoid having to separately provide each magnetic unit with amagnetizable material, the magnetic units may be interconnected by amagnetizable or magnetically conductive material.

For a secure installation of the magnetic unit, the unit may be placedfor instance in a radial bore in the container wall. The radial boreshould be at least deep enough in the radial direction for the magneticunit to be fully insertable without protruding into the interior of thecontainer.

To avoid having to drill a corresponding number of radial bores orsimilar recesses in the container wall while at the same time being ableto simultaneously manipulate a larger number of magnetic units, it ispossible to mount multiple magnetic units in a magnetic-detector insertwhich may be mounted for instance in a circumferential recess on theinside of the container. This recess can again be deep enough to preventthe magnetic-detector insert with the magnetic units from protrudinginto the interior of the container.

Suitably designed magnetic units allow for the deployment in objectswith a variety of cross sections. Of course, for oil exploration andsimilar applications it will be advantageous, and at the same time thedata capture for the detection of the object within the container willbe simplified, if the container and/or object are essentially tubular indesign. In applications related to oil and gas exploration, it is anessentially tubular object that is guided within an equally more or lesstubular container. The object can be so guided that it is either incontact with or moves at a distance from the inside wall of thecontainer.

In another possible, simple and space-saving design, a magnetic unit maybe provided with a ramified and/or continuous helical, electricallyconductive ribbon. Such a ribbon essentially corresponds to a coil andgenerates a comparable magnetic field.

For the convenient manipulation of ribbon-shaped magnetic units of thistype, the ribbon may be mounted on a preferably annular insert. Theinsert, of course, is shaped to correspond to the cross section of thecontainer, permitting easy installation on an inside surface of thecontainer.

The insert can allow for further simplification in that the necessaryelectrical power-supply and/or signal-collecting leads are attached tothe ribbon-shaped magnetic units mounted in the insert.

In analogous fashion it is possible in the case of the aforementionedmagnetic-detector insert employing electrical coils to provide theelectric coils with winding stems as magnetic units. The coils are woundon these winding stems which, like the entire magnetic-detector insert,may consist of a magnetizable material.

The evaluation especially of the signals received by themagnetic-field-sensing magnetic units is possible not only fordetermining the position of the object. A suitably equipped evaluationdevice may include a memory module and/or a display unit or may beconnectable to the latter or for instance to a computer. Stored in thememory module may be the necessary mathematical evaluation algorithmsand/or address tags permitting the analysis of the measured signals. Thedisplay unit may be used, for example, for a graphic illustration of theobject or for detecting the object.

The evaluation device may also be so configured that in addition tomerely detecting the presence of the object it also permits thedetermination of the position, shape, size or direction of movement ofthe object.

The analysis of the signals emanating from the magnetic units and thevery positioning of the magnetic units can be simplified for instance byaligning the magnetic axes of the magnetic units with a longitudinalaxis of symmetry of the container.

BRIEF DESCRIPTION OF THE DRAWINGS

The following describes desirable design examples of this invention inmore detail with the aid of the figures in the attached drawings inwhich:

FIG. 1 is a perspective side view of a first design example of adetection system according to this invention, employing a tubularcontainer;

FIG. 2 is a top view of a horizontal section through FIG. 1;

FIG. 3 is a perspective side view of a second design example of adetection system according to this invention;

FIG. 4 shows a partial vertical section through FIG. 3;

FIG. 5 is a perspective side view of a third design example of adetection system according to this invention;

FIG. 6 is an enlarged illustration of detail “A” in FIG. 5;

FIG. 7 is an enlarged illustration of detail “B” in FIG. 5;

FIG. 8 is a conceptual illustration of a horizontal cross sectionthrough a detection system according to this invention;

FIG. 9 is an illustration as in FIG. 8 with an object in centralposition;

FIG. 10 is an illustration as in FIG. 8 with an object in an off-centerposition;

FIG. 11 is an illustration as in FIG. 8 with an object in anotheroff-center position;

FIG. 12 is an illustration as in FIG. 8 with an object in anothercentral position;

FIG. 13 is a conceptual illustration explaining the magnetic flux; and

FIG. 14 shows in detail an area-array element per FIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts a first design example of a detection system 1 accordingto this invention, with a tubular container 2 and a similarly tubularobject 3. The container extends for instance from an ocean-surfaceplatform, not shown, to a frame section anchored on the sea floor.Inside the container 2 the object 3 is guided in the longitudinaldirection 33 i.e. in the direction of relative movement 14. The objectmay for instance be a section of a drill rod, a tool or similarimplement employed in submarine oil exploration.

In an orientational plane 16 which extends perpendicular to thedirection of relative movement 14, the container 2 accommodates a numberof magnetic units 4 to 9. These are housed in corresponding radial boresof the container 2 and support at least one electric coil 17 each. Thecentral axes of the coils 17 are positioned in the orientational plane16 and point toward the center of the longitudinal bore 36. All magneticunits 4 to 9 are mounted in an equidistant relation to one another onthe inside 15 along the internal circumference of the container 2. Thecoils 17 are positioned within the radial bore 19 so that the magneticunits 5 to 9 will not protrude past the inner surface 15 into thelongitudinal bore 36.

Each coil 17 connects to the appropriate electrical leads 35 whichextend outward away from the container 2 from where they are bundled inomnibus cables, not shown, and run for instance to a topside point.

At least magnetic unit 4 is a magnetic-field-generating magnetic unit.Its magnetic field is modified by the object 3 which at least in partconsists of a magnetizable or magnetically conductive material 18, andthe magnetic field, modified by the movement and changed position of theobject 3 relative to the longitudinal bore 36, can be captured by themagnetic-field-sensing magnetic units 5 to 9. By way of their electricalleads 35, the magnetic units 5 to 9 thus generate a correspondinginduced voltage as a function of the magnetic flux permeating them andchanging with time.

Instead of arranging the magnetic-field-generating magnetic unit 4 andthe corresponding magnetic-field-sensing magnetic units 5 to 9 in onesingle plane 16 per FIG. 1, it is also possible to position themagnetic-field-sensing magnetic units for instance partly or entirely indifferent orientational planes which are spaced at a distance from andoffset upward and/or downward relative to the orientational plane 16 perFIG. 1.

FIG. 2 shows a horizontal section through FIG. 1 in the area of theorientational plane 16 and more specifically in the area where magneticunit 7 is located. The radial bore 19 in a wall 37 of the container 2opens toward the inside surface 15 while at its opposite end a wire duct38 allows the electrical leads 35 to run from the coil 17 to the outsideand away from the longitudinal bore 36. The wire duct 38 can be closedoff with a cap 39 through which the leads 35 are passed via awater-tight seal.

The magnetic-field-generating magnetic unit 4 per FIG. 1 is configuredin analogous fashion. It should be mentioned at this point that allmagnetic units per FIG. 1 are capable of serving asmagnetic-field-generating or magnetic-field-sensing magnetic units. Forexample, magnetic units 6, 7 and 8 may be used as themagnetic-field-sensing units and the magnetic units 4, 5 and 9 as themagnetic-field-generating units. Obviously, any arbitrary assignment ofthese magnetic units is possible both before and during a givendetection process.

FIG. 3 is a perspective view, corresponding to FIG. 1, of a seconddesign example of the detection system 1 according to this invention. Inthis figure and in the figures that follow as well as in FIGS. 1 and 2,identical components bear identical reference numbers which will bementioned only occasionally.

FIG. 3 differs from FIG. 1 by the consolidation of the magnetic units 4to 10 in one magnetic detection insert 20 consisting of a magnetizableor magnetically conductive material 18. The magnetic detection insert 20is suitably mounted in a circumferential recess 21 on the inside 15 ofthe wall 37 of the container 2. The magnetic detection insert 20 has anessentially U-shaped cross section. The open end of the U-profile facesinward in the direction of the longitudinal bore 36. Located at givenpoints in the annular gap 40 between the legs of the U-profile is awinding stem 28 consisting of a magnetizable material and radiallyextending parallel with the U-legs toward the inside in the direction ofthe longitudinal bore 36. Wound onto each such winding stem 28 is a coil17 of the respective magnetic unit 4 to 10. These magnetic units, i.e.coils, are arranged in one orientational plane 16 analogous to FIG. 1.It should be pointed out again that similar magnetic detection insertscan be mounted in more than one orientational plane.

FIG. 4 shows a partial vertical section through the design example perFIG. 3. It clearly illustrates that the coil 17 is wound on the windingstem 28 and that the associated electrical leads 35 of the coil 17 runthrough a hole in the wall 37 to the outside in a radial directionrelative to the container 2. As has been explained in connection withFIG. 1, the various magnetic units 4 to 10 may be optionally set tooperate as magnetic-field-generating or magnetic-field-sensing units.

FIG. 5 is a perspective view, analogous to FIGS. 1 and 3, of a thirddesign example of the detection system according to this invention.

In this design example, the magnetic units 4 to 11 are in the form ofribbons 22 applied on an insert 23 by a thin-film or similar technologyprocess. The ribbons extend in a ramified and/or helical configuration.Each ribbon is provided at one end with an electrical connector 41 andat the other end with a corresponding electrical connector 42 forsupplying power or collecting sensing signals. On the outside of theinsert 23 opposite the longitudinal bore 36 the contacts 41, 42 areconnected, for instance as shown in FIG. 6, to electrical power supplylines 24, 25 or electrical signal-processing lines 26, 27. Theseelectrical lines 24, 25 and 26, 27, for instance as shown in FIG. 7, canbe switched to serve either as power-supply or signal-processing lines,thus affording the option of using the magnetic units.

The insert 23 consists of a thin ring of a magnetizable material whichallows easy mounting on the inside wall 15 of the container 2 inessentially any desired location. Similar inserts 23 can be mounted indifferent orientational planes as described in connection with FIGS. 1and 3.

At one point the insert 23, by way of its leads 24 to 27, is connectedto an evaluation device 12 which in the case of submarine oilexploration is typically located in a suitable place on a surfaceplatform. For other applications of the detection system according tothis invention, such as land-based oil exploration, the evaluationdevice 12 will be set up in a conveniently accessible location.

In the design example per FIG. 5, the evaluation device 12 incorporatesfor instance a memory module 29 for saving the incoming sensing signalsor for storing appropriate programs for the analysis of these sensingsignals. The sensing signals, processed as necessary, can be viewed on adisplay monitor 30 connected to the evaluation device 12. The evaluationdevice 12 may be computerized or connected to a remote computer 31 whichmay also allow the evaluation device to be programmed for instance toswitch the magnetic units into the magnetic-field-generating or,respectively, magnetic-field-sensing mode.

At this juncture it should be mentioned that themagnetic-field-generating magnetic units may also be in the form ofpermanent magnets, for one example. The magnetic-field-sensing magneticunits on their part may be in the form of magnetic sensors such as Hallelements.

The evaluation device 12 also offers the possibility to change thepolarity or field intensity of the magnetic field generated. Alternatingmagnetic fields can also be produced.

FIGS. 8 to 12 are conceptual illustrations of the detection system 1according to this invention, showing different magnetic units 4 to 11without an object 3 (FIG. 8) and, respectively, with different objectsin different positions within the container 2.

FIG. 8 shows the magnetic field generated by the magnetic unit 4,unaffected, as in Figure 1, by any object 3. The correspondingmagnetic-field flux lines 43 extend perpendicular to the longitudinalbore 36 and flow to the respective magnetic-field-sensing magnetic units5 to 11. The distance of the magnetic-field-sensing magnetic units 5 to11 from the magnetic-field-generating magnetic unit 4 determines theextent to which the flux lines permeate the magnetic units. The magneticflux itself varies accordingly.

The magnetic units 4 to 11 are arranged in a way that they, and inparticular their respective magnetic axes 32 as shown for instance inFIG. 9, are oriented toward a central point 34 in the longitudinal bore36, i.e. toward an axis of symmetry 34 which extends in the longitudinaldirection 33 per FIG. 1.

When an object 3 moves relative to the container 2, the result will be achange in the path of the magnetic flux lines, as shown in FIGS. 9 to11. In FIG. 9 the object 3 is positioned at dead center 34, causing acorrespondingly symmetrical flux-line distribution pattern. In FIG. 10,the object is situated off-center and close to themagnetic-field-generating magnetic unit 4.

In FIG. 11, the object 3 is again in an off-center position, in thiscase close to the magnetic-field-sensing magnetic unit 9.

From the respective changes in the magnetic fields and the magneticflux, detectable by the magnetic-field or magnetic-flux-sensing units 5to 11, conclusions can be drawn as to the presence of the object 3 inthe vicinity of the magnetic unit as well as the distance between theobject 3 and the individual magnetic units, the orientation anddimensions of the object 3 and its direction of movement. By means ofappropriate imaging processes in the evaluation device 12, for instanceas shown in FIG. 5, it is possible to view on the display monitor 30 theobject 3, its position, orientation, size and movement.

FIG. 12 shows an object 3 larger in overall dimensions and wallthickness, with corresponding changes in the magnetic field and magneticflux pattern. FIG. 12 thus shows what other conclusions are possible interms of the dimensions of the object 3.

FIG. 13 is a simplified representation of a magnetic-field-generatingmagnetic unit 4, the magnetic field and flux line 43 generated by it,and the respective magnetic flux 13 through different area-arrayelements 44. Traditionally, the magnetic flux is determined by thefollowing equation:

ϕ = ∫_(Δ)Bx𝕕Awhereφ is the magnetic flux, B is the magnetic induction and dA is aninfinitesimal vectorial area-array element. According to the invention,the magnetic units 4 to 11 are so arranged that the respective magneticflux displays its maximum value perpendicular to the relative movementbetween the object and the container, meaning that the scalar productderived from magnetic induction and the vectorial area-array elementtakes on its maximum value for the respective area-array elements perFIG. 13.

FIG. 14 is a conceptual illustration showing that for each area-arrayelement 44 the magnetic flux derives from the scalar product of magneticinduction B und ΔA as the vectorial area-array element. The applicableequation is a follows:φ=|β|x|ΔA|x cos αwhereα is the corresponding angle 46 between the vectors B and ΔA.

The following will briefly explain the operating mode of the detectionsystem according to this invention with reference to the attacheddrawings.

By way of the magnetic flux and/or the magnetic attenuation, thedetection system according to this invention measures any given objectof any given shape, orientation, position and geometry within a magneticfield generated inside a container 2. One or several magnetic unitsserve to generate the magnetic field and the corresponding magneticflux. One or several additional magnetic units capture the magnetic fluxthat has been modified by the object and its movement or location and onthe basis of the sensing signals received it is possible to determinethe distance between the object and these magnetic units as well as theposition, size and direction of movement of the object. Themagnetic-flux-based measurement can take place in static and/or dynamicfashion through alternating fields, variable field intensity andvariable polarity.

The magnetic-field-generating magnetic units may be in the-form forinstance of a permanent magnet or electrically powered and controlledcoil. The magnetic-field-sensing magnetic units can measure the magneticflux produced in static fashion employing Hall elements and/or indynamic fashion by way of electromagnetic induction. The configurationand the number of the magnetic-field-generating andmagnetic-field-sensing magnetic units are variable, and especially whencoils are used as the magnetic units a switchover between themagnetic-field-generating and the magnetic-field-sensing mode of themagnetic units is easily accomplished.

The sensing signals are evaluated using mathematical operations and/oraddress tags and it is possible to display them in graphic form on adisplay monitor per FIG. 5, showing the shape and position of the objectunder analysis.

The magnetic units can be arranged in a circular or other configurationin one or several planes and they are typically interconnected via amagnetically conductive or magnetizable material. The multiplicity ofthe different magnetic units and their utilization for generating orsensing and measuring magnetic fields produce magnetic flux patternsbetween all associated magnetic units which patterns, and any changesthereof, are used for the imaging and positional determination of theobject to be measured. The varying magnetic flux is analyzed byappropriate metrics for a determination of the size, shape and positionof drill pipes including their tool joints and any associated tools. Itis also possible to detect the direction when the pipes or toolsconstituting the objects within the tubular container are moved. Themagnetic units can further recognize drill pipes which are in contactwith one of the inside walls of the container, causing the dreadedfriction-induced wash-out of the equipment.

1. A system, comprising: a container; an object that moves within thecontainer; and a magnetic-based position detection system that isconfigured to determine a longitudinal position of the object relativeto the container and a transverse position of the object relative to thecontainer based on a plurality of magnetic units circumferentiallyintegrated with the container.
 2. The system of claim 1 wherein thecontainer comprises a tubular structure that extends from anocean-surface platform to a sub-sea location.
 3. The system of claim 1wherein the object comprises an oil exploration tool that moves withinthe tube.
 4. The system of claim 1 wherein the magnetic-based positiondetection system comprises an evaluation unit coupled to a plurality ofmagnetic units comprising at least one magnetic field generating unitand a plurality of magnetic field measuring units.
 5. The system ofclaim 4 wherein the at least one magnetic unit is positioned on theobject and the plurality of magnetic field measuring units arepositioned on an inside area of the container.
 6. The system of claim 4wherein the at least one magnetic unit and the plurality of magneticfield measuring units are positioned on an inside area of the container.7. The system of claim 4 wherein, to determine said longitudinalposition and said transverse position, the evaluation unit selectivelycauses at least one of the magnetic units to switch between a magneticfield generating mode and a magnetic field measuring mode.
 8. The systemof claim 4 wherein, to determine said longitudinal position and saidtransverse position, the evaluation unit selectively controls a polarityof at least one of the magnetic units.
 9. The system of claim 4 wherein,to determine said longitudinal position and said transverse position,the evaluation unit selectively controls a magnetic-field intensity ofat least one of the magnetic units.
 10. The system of claim 4 wherein,to determine said longitudinal position and said transverse position,the evaluation unit selectively alternates a magnetic field produced byat least one of the magnetic units.
 11. The system of claim 4 whereinthe evaluation unit causes the longitudinal position and the transverseposition to be displayed on a monitor.
 12. The system of claim 4wherein, to determine the transverse position, the evaluation unitreceives magnetic flux measurements from the plurality of magnetic fieldmeasuring units and correlates the received magnetic flex measurementswith the transverse position.
 13. The system of claim 1 wherein themagnetic-based position detection system comprises an evaluation unitcoupled to a plurality of magnetic units arranged in a single planearound an internal circumference of the container.
 14. The system ofclaim 1 wherein the magnetic-based position detection system comprisesan evaluation unit coupled to a plurality of magnetic units arranged inmultiple planes around an internal circumference of the container. 15.The system of claim 1 wherein the magnetic-based position detectionsystem comprises an evaluation unit coupled to a plurality of magneticunits, wherein the evaluation unit selectively provides power to andreceives measurements from at least one of the magnetic units.